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This paper presents results of a reduced (1:8) scale experiment investigating the performance of hybrid structural (gray) and natural-based (green) infrastructure for wave overtopping reduction. Experiments were scaled to a 1:8 geometric scale based on 1:2-scale experiments conducted during the Summer of 2023 at Oregon State University. Seven wave conditions were tested, with (model-scale) wave periods ranging from 1 to 2 seconds and wave heights ranging from 6.0 to 7.5 cm. These wave conditions were conducted throughout two configurations: a seawall-only (baseline) configuration and a configuration with the seawall in combination with a mangrove forest installed seaward of the wall. The total volume of overtopped water was measured for each wave condition. Results indicated that adding mangroves reduced overtopping for all wave conditions, with an average of 32.1% reduction in overtopped volume compared to the baseline configurations. This reduction falls within the range of preexisting overtopping rates. Results from these experiments can assist engineers in understanding the performance of hybrid coastal infrastructure to design effective and sustainable shoreline protection.
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Physical model comparison of gray and green mitigation alternatives for flooding and wave force reduction in an idealized urban coastal environment
A 1:16 scaled physical model was constructed to investigate the effectiveness of a seawall, a submerged breakwater, and mangrove forests to mitigate overland flooding and forces on structures in an idealized urban coastal environment. The experiment was performed using tsunami-like waves at different water levels, wave amplitudes, and time scales to simulate long-wave dynamics. The baseline condition (no mitigation), seawall, submerged breakwater, and mangrove forest were tested individually, and the seawall and submerged breakwater were also tested in combination. Wave gauges, acoustic Doppler velocimeters, loadcells, and pressure gauges were used to measure wave elevations, velocities, forces, and pressures on coastal structures, respectively. The performance of these hard structures and mangroves was compared through their effects on wave elevation, particle velocity, and force reduction. Experimental results showed that each protecting structure reduced the horizontal wave forces and inland flow hydrodynamics in the low-water-level case, with a similar performance by the individual seawall, submerged breakwater, and four rows of mangroves. The combined configuration, when the seawall and submerged breakwater were installed simultaneously, caused the most significant maximum force percent reduction by approximately 50%, while mangrove forests arranged in eight rows resulted in a force reduction of 46% in the first building array. However, in the high-water-level cases, the impulsive force measured with the presence of the submerged breakwater was larger than in the baseline case; thus, the submerged breakwater may amplify the impulsive force on the vertical building rows for certain incident wave conditions. Generally, the combined hard structures induced the lowest force reduction factor measured in almost every building row compared to the seawall, submerged breakwater, and mangroves considered separately for all wave conditions and water levels. That means this multi-tiered configuration showed better performance than individual alternatives in reducing horizontal forces inland than the individual alternatives considered separately.
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- PAR ID:
- 10487520
- Publisher / Repository:
- Coastal Engineering
- Date Published:
- Journal Name:
- Coastal Engineering
- Volume:
- 184
- Issue:
- C
- ISSN:
- 0378-3839
- Page Range / eLocation ID:
- 104339
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.coastaleng.2023.104339
